The present invention relates to a drive transmission mechanism for transmitting the rotational driving force of a drive shaft connected to a motor or like drive source to a driven shaft on speed reduction or increase.
A gear mechanism, transmission mechanism comprising a pair of toothed pulleys and a timing belt, or the like is most widely used for transmitting the rotation of a drive shaft to a driven shaft. When a great reduction ratio or increase ratio is required for the transmission, mechanisms comprising, for example, a plurality of idle gears each having two spur gears and different from one another in gear ratio are generally used.
FIG. 5 shows an example of such mechanism. With reference to the drawing, indicated at 101 and 101' are upright inside plates provided in the interior of an apparatus. A motor 102 serving as a drive source is mounted on the inside plate 101. A specified number of intermediate shafts 103 are fixed, each at its one end, to the inside plate 101', which also supports a driven shaft 105 by a bearing 104 rotatably.
The drive shaft 102a of the motor 102 fixedly carries a drive gear 106 to rotate the gear therewith. Similarly, a driven gear 107 is fixed to the driven shaft 105. An intermediate gear 108 is mounted on each of the intermediate shafts 103 and is rotatable relative to the shaft 103. The intermediate gear 108 comprises a large gear 108a and a small gear 108b integral with the gear 108a and different therefrom in diameter. The large gear 108a of the intermediate gear 108 most proximate to the drive shaft 102a is in mesh with the drive gear 106, and the small gear 108b of this intermediate gear 108 is in mesh with the large gear 108a of the second intermediate gear 108. Through similar meshing engagement between the other gears including the small gear 108b of the last intermediate gear 108 in mesh with the driven gear 107, the drive shaft 102a is coupled to the driven shaft 105.
With the above mechanism, the rotation of the drive shaft 102a of the motor 102 is transmitted via the drive gear 106, the plurality of intermediate gears 108 and the driven gear 107 to the driven shaft 105 upon a great reduction.
FIG. 6 shows another mechanism wherein toothed pulleys and timing belts are used in place of the above gears.
With reference to the drawing, a drive pulley 109 is fixed to a drive shaft 102a, and a driven pulley 110 to a driven shaft 105. An intermediate pulley 111 of a double structure having a large pulley 111a and a small pulley 111b is rotatably supported on each of intermediate shafts 103. The drive pulley 109 is coupled to the large pulley 111a of the first intermediate pulley 111 by a timing belt 112, the small pulley 111b of the first intermediate pulley 111 to the large pulley 111a of the second intermediate pulley 111 by another timing belt 112, and the small pulley 111b of the second intermediate pulley 111 to the driven pulley 110 by another timing belt 112.
With this mechanism, the rotation of the drive shaft 102a is also transmitted to the driven shaft 105 upon a reduction as in the case of the mechanism of FIG. 5.
However, the mechanisms of FIGS. 5 and 6 have the following problems to be solved.
With the mechanisms described, the intermediate gears 108 or the intermediate pulleys 111 need to be supported by the respective intermediate shafts 103, so that a larger space is required with an increase in the number of gears or pulleys, making it difficult to compact the body of the apparatus including the mechanism. The mechanisms further have the drawback of being complex in construction, necessitating many shafts and therefore being costly.